This invention involves a low cost, high value woven fabric useful as a primary backing for tufted pile carpets. More specifically, the invention pertains to a woven fabric composed in both the warp and the weft directions of filmy elements in the form of longitudinally-oriented splittable ribbons formed from a blend of a major amount of polyester and a minor amount of a polyolefin, said elements having been heat-treated at a temperature of at least 150.degree. F. (66.degree. C.) for a sufficient time to render the elements splittable. Preferably the polyester is polyethylene terephthalate and the polyolefin is polyethylene. An advantage of the invention is that inexpensive polyester such as that recoverable from waste bottles, fibers and films is abundantly available and provides a satisfactory source of raw material.
Woven jute carpet backing has been replaced to a large extent in recent years by products made from synthetic materials. Carpet backings woven from ribbons of polypropylene, such as those disclosed in Rhodes U.S. Pat. No. 3,110,905, are the current industry standard, partly because they are strong yet inexpensive, and partly because they split longitudinally when penetrated by a carpet tufting needle. The ability to split longitudinally is highly desirable, because split ribbons close and grip the yarn securely after the needle retracts, keeping the yarn tufts firmly in position. The splitting prevents the ribbons from being severed transversely or from being severely weakened in the longitudinal direction by the penetration and removal of the tufting needles. While such products have been successful to a large extent, polypropylene has not altogether been satisfactory as the material forming the ribbons as it has the disadvantage of not being dyeable by standard carpet dyes, thus making the backing more visible and the carpet less attractive. In addition, polypropylene has a tendency to shrink at temperatures used for forming automotive carpets to desired contours and at temperatures used in bonding carpet tiles.
Polyester backings, readily dyeable with dispersed dyes and thermally stable at higher temperatures, largely overcome these particular deficiencies, and indeed spunbonded polyester backings are currently used for both automotive carpets and carpet tiles. These backings, however, are less satisfactory than those of polypropylene because they often do not grip the tufts with adequate force, and they are quite expensive. The Rhodes patent referred to above and Dionne U.S. Pat. No. 3,317,366 each describe all-polyester backings, but both tend to have the same tufting deficiencies as spunbonded backings. Rhodes discloses fabrics woven from ribbons in both directions, but the ribbons are not said to be splittable. The Dionne backing is made from flat warp ribbons and multifilament weft yarns. No mention is made of the splittable or nonsplittable nature of the warp ribbons. Without the advantages created by splittable ribbons, these polyester backings will not perform as well as polypropylene backings in firmly securing the fiber tufts in place.
Various backings which are more splittable have been suggested in an attempt to overcome the disadvantages of polypropylene while maintaining its positive features. Stitch bonded backings, made by stitching layers of splittable film or by stitching layers of a splittable film and a nonwoven, are disclosed in Ploch et al., U.S. Pat. No. 3,769,815 and Kumar, U.S. Statutory Invention Registration H90 respectively. However, these materials have high cost and poor strength in the fill or cross machine direction. A woven backing made from a blend of 80% to 65% polyamide with 20 to 35% polyester is shown in Ramsauer et al., U.S. Pat. No. 4,010,303. This is primarily a polyamide backing and has several drawbacks: (1) it is very susceptible to moisture; and (2) the ribbons, if not splittable (particularly those in the weft direction), rupture transversely when impacted by a tufting needle. This makes for an expensive and deficient backing.